This invention relates to continuously operating sedimentation tanks of the type wherein a sludge conveying rake arm structure is supported for rotation about a vertical axis upon a center pier.
The rake arm structure may be of a kind that comprises a central vertical cage portion surrounding the pier, and a plurality of horizontal rake arms extending from the cage portion, each arm being provided with a series of sediment engaging plowing blades. Rotation imparted to the rake structure would cause the bladed arms to convey the sediment or sludge over the tank bottom to an annular sludge collecting zone or sump surrounding the pier, for discharge therefrom by a sludge withdrawal pump.
The upper end of the cage portion has fixed thereto a bull gear concentric with the vertical axis of rotation. This gear is supported by an annular bearing structure mounted concentrically upon the top end of the pier. The bearing is constructed and arranged for sustaining the vertical load of the rake structure, while also capable of absorbing radial stabilization pressures.
One or more interbalanced pinion drive units incorporated in the bearing structure impart the required driving torque to the bull gear and thus to the rake structure for moving the sludge to the discharge zone around the pier.
More in particular this invention is concerned with mounting upon the pier a drive head of the kind whereby the rake structure is supported floatingly or hydrostatically upon horizontal oil pressure areas or pads spaced from one another in an annular trough structure or frame or base.
Provision is also made for radially facing oil pressure areas or pads in the trough structure, for radial stabilization guidance of the rake structure.
Such hydrostatic bearing arrangements for the rake structure are free of mechanical wear and tear, while avoiding problems of manufacturing accuracy and wear and tear or possible failure, as may be encountered with large diameter mechanical ball or roller bearings.
With the improved and simplified version, according to this invention, the range of applicability of the present bearing construction is economically applicable within a wide range of sizes or bearing diameters.
A forerunner of an hydrostatically supported and guided rake structure is disclosed in U.S. Pat. to Raynor No. 3,498,468, wherein an annular hydrostatic bearing or drive head of large diameter, is mounted atop a caisson type hollow center pier. The drive head in the earlier construction comprises an annular runner having torque transmitting connection with the vertical cage structure, concentric therewith. The runner has at the bottom an horizontal annular bearing face whereby the weight of the rotating rake structure is supported hydrostatically upon the oil pressure bearing pads through an oil film supplied by the oil pressure pads. A cylindrical bearing face cooperates with radial hydrostatic bearing pads. The bull gear itself is connected to the top of the annular runner which latter thus represents a torque transmitting connection between the bull gear and the rake structure.
The interior of the caisson structure of the pier provides room and access to various accessory equipment, such as the sludge pump located at the bottom of the pier. The intake end of this pump communicates directly with the sludge collecting zone surrounding the foot end of the pier, thus allowing for gravity intake of the sludge under the static head of the liquid body in the tank.
Thus, the sludge pump needs to deliver only against a moderate pressure head, upwardly through the open central area surrounded by the annular drive head, and then horizontally across an acess bridge leading from the pier to the peripheral wall of the tank, for further disposal.
Other accessory equipment that can be accommodated within the space available within the caisson structure of the pier, may comprise a standby sludge pump, as well as a pumping system for supplying the required oil pressure to the oil pressure pads, in order that the weight of the rake structure may be supported hydrostatically, or floating upon a film of oil. Also accommodated in the caisson type pier are stairway structures providing access to various operating platform levels.
The annular main trough or base structure containing the oil pressure bearing pads collects the spent hydrostatic pressure oil for return to an oil reservoir. In this base structure, an auxiliary annular trough is connected unitary to the base structure concentric with the main trough, containing a separate bath of lubricating oil for the bull gear and the drive pinions engaging them.
Suitable annular sealing means embodied in such a drive head will protect the oil in the hydrostatic pressure oil system, as well as the oil in the gear lubricating trough, against contamination.
One object of this invention is to provide an improved hydrostatic bearing system or drive head for the pier supported rake structure, that is economically and structurally simplified, and yet of great rigidity, high load carrying capacity and compactness and economically adaptable for a wide range of bearing diameters and torque loads.
For the purpose of attaining the above stated objective, the invention provides a hydrostatic bearing construction for the drive head herein briefly termed a hydrostatic drive head, featuring a specially designed internally toothed bull gear provided with an outer overhanging rim portion the underside of which is shaped to surround the oil pressure pads, so as to be vertically supported, as well as to be radially guided thereby.
Accordingly, this rim portion is formed with a downwardly open annular recess providing an internal horizontal bearing face cooperating with vertical load sustaining oil pressure pads, and also formed with an internal cylindrical bearing face conforming to the curvature of the radially effective guiding oil pressure bearing faces.
Further, according to the invention, the vertical load carrying oil pressure pads have an oil pumping system separate from one that is provided for the radially stabilizing oil pressure pads, providing higher operating pressure for the load carrying pads, and only lower pressure needed for the radial stabilizing pads.
In a preferred embodiment there are twice as many load carrying oil pressure pads than there are radial stabilizing oil pressure pads. On that basis an economical pressure pad arrangement is attainable by having dual purpose oil pressure pads or blocks alternating with single purpose pressure pads or blocks.
In this connection, a dual purpose oil pressure pad or bearing block comprises an horizontal hydrostatic load carrying area, as well as a radially effective stabilizing hydrostatic bearing area, each with its separate oil pressure supply.
The single purpose pressure pad or block provides only hydrostatic support for its portion of the vertical load, but lacks the provision for radial hydrostatic pressure stabilization.
The spent hydrostatic pressure oil from both pressure systems may drain into an annular reservoir or receiver integrated into this base structure in concentric relationship therewith.
Specific features are found in a preferred and compact novel form of the base structure preferably in the nature of a casting of integral construction.
Compactness of this structure and thus of the drive head as a whole is attained also by having the annular base trough structure integral with an annular hydraulic oil reservoir, thus eliminating the need for return connections for the hydraulic oil to a separate reservoir.
This base structure or casting comprises an intermediate annular horizontal body portion or platform portion greatly reinforced by cylindric concentric walls extending therefrom in opposite directions. The upwardly extending walls constitute with said body portions an annular trough structure accommodating the rotating bull gear, as well as the associated stationary system of hydrostatic load supporting pads and of radially effective hydrostatic stabilizing pads. A pair of concentric walls extending downwardly from said annular body portion, constitute together with an annular bottom closure plate, the aforementioned annular reservoir. This annular reservoir greatly contributes to the total rigidity and integrity of the base structure.
According to one embodiment, the annular trough structure comprises two separate concentric troughs for the bull gear and for the hydrostatic pads respectively, whereby the lubrication of the internally toothed bull gear and its drive pinion is effected separate from the operation of the hydrostatic pads.
According to another embodiment the annular trough structure is designed to provide for the use of a single oil supply capable of serving for gear lubrication as well as for the operation of the hydraulic pads. That is to say, such a dual purpose or multi-purpose oil is applied and recirculated to both the gear and the hydrostatic pads.
From the foregoing features of the hydrostatic bearing as far as they pertain to the base structure or load supporting frame, it will be understood that the inner upstanding wall thereof is formed so as to accommodate the drive pinions for the internally toothed bull gear.
According to another feature, a substantially flat horizontal adaptor ring of special construction is bolted to an inwardly overhanging horizontal flange of the inner upstanding wall of the casting. This adaptor ring has an outer diameter large enough to provide an outward annular overhang having annular sealing relationship with the annular top end face of the gear. This inner seal located at an upper level, cooperates with an outer annular seal effective at a lower level between the outer edge portion of the load supporting rim portion of the gear and the adjoining outer peripheral edge of the horizontal annular body portion of the base structure.
This adaptor ring is shaped to match the shape of the base structure, to accommodate the drive pinion extending therethrough. This adaptor ring provides not only the aforementioned inner seal at the upper level, but also a horizontal top reference plane for the mounting thereon of the gear housings of the respective drive pinions.
Still other features are found in the provision of novel torque transmitting and weight supporting connections between the bull gear and the central cage portion of the rake structure.
Other features and advantages will hereinafter appear.